Known motor shafts are attached to the rotor of an electric motor by applying heat fitting. The rotor includes a plurality of rotor disks, which have a shaft hole that has a slightly smaller diameter than the shaft. When heated, the shaft holes of the rotor disks expand allowing the disks to be positioned around the shaft. When the disks cool down to the same temperature with the shaft, a tight attachment is achieved as the disks shrink.
FIG. 1 shows an assembly of a shaft and a rotor disk in accordance with a known arrangement. As shown in FIG. 1, a fitting between a rotor disk 100 and a motor shaft 112 in a known implementation. As shown in FIG. 1, the motor shaft 112 is tightly placed into a shaft hole 110 of the rotor disk. The assembly of FIG. 1 shows a positioning hole 120 to which a positioning pin 140 has been placed.
Heat fitting is applicable to situations where the rotor material tolerates heating to a high temperature and consequent high mechanical stresses due to heat expansion. However, the process of heat fitting includes several steps and extra tensions remain in the rotor. Use of heat fitting is often not possible and other ways to provide the friction force between the shaft and the rotor disks should be considered.
Such other ways include cold fitting by pressing, which, however, is disadvantageous because the fit easily remains loose and the rotor disks may bend while pressed. In still another known method, the disks are mounted by using wedges fitted to wedge grooves in the disks, which also adds worksteps to the procedure. Gluing of the disks to the shaft has also been used, but longterm endurance of such a fitting is questionable.